1. Field of the Invention
The present invention relates to a magnetic detection apparatus for detecting the rotational position of a magnetic moving member that is formed on its periphery with teeth and rotates in a circumferential direction, for example.
2. Description of the Related Art
FIG. 13(a) is a perspective view of a known magnetic detection apparatus. FIG. 13(b) is a partial plan view of the magnetic detection apparatus of FIG. 13(a). FIG. 14 is an electric circuit diagram of the known magnetic detection apparatus. FIG. 15 shows operational waveform diagrams of the known magnetic detection apparatus.
The magnetic detection apparatus includes: a processing circuit 20 arranged apart from a magnetic moving member 1 on a plane thereof, which is formed on its periphery with teeth 1a and rotates around an axis of rotation or rotation shaft 4 in a circumferential direction, the processing circuit 20 having a bridge circuit in the form of a magnetoelectric conversion element composed of a magnetoresistive segment 2a and a fixed resistor 12b, another bridge circuit composed of fixed resistors 12c, 12d; and a magnet 3 that applies a magnetic field to the magnetoresistive segment 2a and also applies a magnetic field to the magnetic moving member 1 in the direction of the axis of rotation thereof. In addition, the processing circuit 20 incorporates therein an amplifier circuit 13, which amplifies a signal whose voltage is varied depending on a change in the resistance of the magnetoresistive segment 2a, a comparison circuit 14 and an output circuit 15.
With the magnetic detection apparatus as constructed above, the magnetic moving member 1 is caused to rotate in synchronization with the rotation of the rotation shaft 4, so that the magnetic field applied to the magnetoresistive segment 2a from the magnet 3 is accordingly varied. As a result, the resistance value of the magnetoresistive segment 2a changes between the time when a tooth 1a of the magnetic moving member 1 comes to face the magnetoresistive segment 2a and the time when a groove 1b of the magnetic moving member 1 comes to face the magnetoresistive segment 2a, as illustrated in FIG. 13. Thus, the output of the amplifier circuit 13 also changes accordingly. Then, the output of the amplifier circuit 13 is waveform shaped by means of the comparison circuit 14, so that the output terminal 16 of the processing circuit 20 finally generates a final output signal of “1” or “0” corresponding to a tooth 1a or a groove 1b of the magnetic moving member 1.
However, the known magnetic detection apparatus as described above has the following problem. That is, as shown in FIGS. 16(a) and 16(b), when intervals between adjacent teeth 1a and the circumferential width of each tooth 1a are both small, and when an opposing space (hereinafter called a “GAP”) between the circumferential surface of the magnetic moving member 1 and the magnetoresistive segment 2a is large, as shown in FIG. 14, there might often arise such a case where a final output signal of “1” or “0” is not obtained from the output terminal 16 of the processing circuit 20, as shown in FIG. 15.